Gas discharge display panels are provided with circuitry for producing a sustain voltage (typically 200 v) which is applied to each of the discharge cells in the display panel. The sustain voltage causes selected panel areas to discharge at a rate determined by the sustain voltage frequency. In this manner, the selected panel area has the appearance of being continuously illuminated.
A problem associated with the use of large gas discharge display panels is that of power consumption and generation of large sustain voltages. Sustain waveform generator circuits for large gas panel displays can be designed to use power MOS-FET's rather than bipolar transistors to thereby reduce power consumption and avoid the storage and gain problems associated with high voltage-high current bipolar transistors. The use of low cost power MOS-FET's would therefore reduce system hardware and operating costs. Unfortunately, 200 volt FET's are not readily available and have not been found to provide satisfactory operation in a sustain driver.
Four 100 volt FET's in a bridge configuration as illustrated in FIG. 1 can provide a 200 volt swing using a single 100 volt source. While FET's are shown in FIG. 1, bipolar transistors can alternatively be employed as in the case of the IBM 240/480 Gas Panel Program. The voltage is alternatively delivered from one of FET's 10 or 20 to one of driver modules 30 or 35. One of the FET's 15 or 25 is provided to ground the other of the two driver modules 30 or 35 such that when FET 10 is biased "on" to provide source voltage to horizontal driver 30, FET 20 is biased "off" and FET 25 is biased "on" to place the vertical driver module 35 at ground potential. FET 15 must be biased "off" so that the horizontal axis can float to provide the required 100 volt potential between horizontal and vertical driver modules 30 and 35. The 200 volt voltage swing across panel cell 40 is accomplished by reversing the biases on FET's 10, 15, 20 and 25. While this technique will provide the proper voltage to sustain the cell discharge, it requires that both the horizontal and vertical axes float. This greatly increases the vertical data load time and thus the panel update time.